Central-blast rectifier and water temperature controlling means therefor



Aug. 20, 193:5. A L ATHERTN 2,011,605

CENTRAL BLAST RECTIFIER AND WATER TEMPERATURE CONTROLLING MEANS THEREFORFiled Jan. 28, 1952 Z SheetS-Sheet 1 iJgij /z 26' 24 /8 I A324 25 z 4a 21 L 54 l I INVENTOR -WITNESS ATTORNEY Aug. 20, 1935. A. L. ATHERTON2,011,605

CENTRAL BLAST RECTIFIER AND WATER TEMPERATURE CONTROLLING MEANS THEREFORFiled Jan. 28, 1952 z Sheets-Sheet 2 ATTORNEY Patented Aug. 20, 1935 TE'ENT OFFICE CENTRAL-BLAST RECTEFIER AND WATER TEMPERATURE CONTROLLINGMEANS THEREFOR Alfred L. Atherton, Verona, Pa., assignor to WestinghouseElectric & Manufacturing Company, a corporation of Pennsylvania 7Application January 28, 1932, Serial No. 589,415 1'7 Claims. (01.250-275) My invention relates to means for improving simultaneouslyoperating arcs in the same the operation andreducing the spacerequirechamber. ments of mercury-arc metal-tank rectifiers and Thepresent invention it hasparticular relation to means for influencisbased upon thetheory ,5 ing or controlling the flow of vapor in amultiinsulating gas pathsin a rectifier, which causes anoderectifiertank and for providing a blast them to break down, occasionally, atvoltages of of. sufliciently deionized vapor in the region of the orderof or less,'of their ordinary breakthe anodes to prevent arc-backs,while helping down potential, is attributed to the presence of i toprovide sumcient vapor for the main arc path. ionized mercury vapor f omthe a c-pa s 10, The thought behind my invention is to provid otheranodes which are active at the moment. means for preventing a phenomenonwhich con- This ionizedmercury p a o g to my D stitutes a peculiardifierenc e between. the insulat- 911T belief, s a r ed about in aVariable and ing gas paths from the cathode to the anodes e or less n ld way y th last f (and from one anode t th when t parmercury vapor fromthe cathode, in rectifiers as '15 insular anode is notcarrying current th heretofore constructed. Atintervals there will some other anode isactive, on the one hand, and be the combination of a Sufiicienfi densityof an ordinary insulating gap in a s, o 'th th ionization concentratedin the space around an h In y r ctifi r the Object is, of com-Se, anodeon which the reversepotential is applied 1 to have the gas paths betweenthe inactive anodes With Sufiicient instantaneous potential to cause andthe other parts of the structure f m the breakdown wh chdevelops into anarc-back. the function of insulators toprevent current fiow lScomblnatlon of circumstances occurs only to and from said inactiveanodesduring the por- Occaslonany because 1t reqllllfes h acculllulatlon tionor" the cycle Whenthey are not supposedto i gg 3 3: 2 5 2 22 fi n3: 2

r" rre t. If itwere not for the resenoe Y 25 gi gg gn orjanodes carryingcufrent as cause the movement of the'positive ions is conthe terminal ofan arc or'arcs, in the same tank, l d y blast vapor m h cathode stand apotential of somew ere around 10,000 volts, with the spacings, vaporpressures, and mai Into i i g of a large terials of the anodesand thegas, commonly met 2 32 5 2 gi g; 5 2 2 2 etc 0 fifii gi i 'f Wimetal'ta'n'kiecmfiers' 3 m lectlfiet plication is introduced by the factthat along the inwh1ch the maximum potential dlfference 1s path of flowof the Vapor there are portions in of order 9 9 volts no fi should whichenergy losses take place because of the flow ever occur, but 1t1s Wellknown-that such backfires, or arc-backs, do occasionally occur. The 9 Fcurrent" Whlch r t local h theory has been suggested that the remanent22:2 :25 gifg j if gpg gg gg and ionization; which remains in the regionof an The conception that thgsourceof the'se Ceca? q f alter P'tgrmmatlop thls penqd sional breakdowns is the concentration of ioniza-40 activity explains these occas onal back-fires, and tion from anoutside source b1 ought about b means have been added with the view ofquickly r y deicnizm thmse remanem ions the flow, into the highvoltage-gradient space, of

v g 1 i an abnormally large concentration of positive observation hashowever that; the ions, seems to me to be reasonable. It also seemsback-fire m PQ f f Phemmemn, to me to be reasonable that the extremelyvaried d my 5 Of t b fiw of arc-backs flow of gas, resulting from thehigh velocity and during the period of inactivity have not shownextremely irregular path will explain the long a conslderable F e y ines 'F time intervals and the variation in time interinltialremanentomzation period of transltlon vals, rem conductivity toinsulation characteristics Considerations Such as the foregoing lend i agljen path y, F 9 m creased support to the corrective measures dismd,that the remanefit 10111294111011, at least 111 closed in my applicationSerial No. 560,722, filed the mod n typ s f fi a Ordinarily n- September2, 1931. If we can intr'oduce such a struoied, although a ContributoryCause f a flow of tin-ionized vapor that the ionized vapor fire, Cannfita'pledominant e f b cannot" enter the high-gradient portion; ,this

fire in the presence of ionization from" other source of aroing' backis'removed. Inthe rectior belief that the peculiar characteristic of the tosupply the flow of un-ionized vapor.

' My present invention is partly in the nature of-a continuation, inpart, of. my above mentioned application, and, in part, it isdirected'to modifications and improvements thereon.

to a separate mercury pool, and I havedis covered', more definitely, thecontrol of the temperature gradients within the rectifier, if theun-ioniizedeblast is to beused'" effectively,whether itoriginates fromthe oathode poolor from an auxiliary mercury pool. Of course, it isknownthat there are. many 7 other cases of arc-backs, each of"which'hasto For example, the presence 7 be taken care of. of toomuchforeign gas will cause troubleand it fis necessary tog'et-this-kindof thing under control, regardless of what other mechanismsof"vapor-flow" may besetup; The {propen design f and controlof means forproviding an'un-ionized mercury; blast, in accordance with my presentinvention, afiords one of the most effective ways of "which 1' know,

for avoiding the troublesdue to foreigngaso This maybe explained asfollows gas'which is givenoff, 'therebydepositing' said 7 foreign gasat.-a portion of -vacuum pumping connection isfmade. This re-: 1sults-in ireeingthe space within the anode shield from entranceofserious quantities 'of foreign .-.ga i W are carried along'in I vaporflow an'dhavefaccumulated in pockets, in. previous constructions;thereby preventing, the mercury vapors from .the tank, thus lowering theefliciency ofthe recti-" lier, bu Whatis worse, wagary. of thevaporpufiwthrough-such agas pocket and blows the Thevapor from thecathode may be assumed to be relatively free from foreign gas. .Theprincipal sources of foreign gas, assumingthat Iany'rubber gasketsiwhich arejutilized' ior vacuum-sealing processes are *s'ufiicientlycooled, I are the anodes andthe hot parts'surrounding them. I believethat-"these gases, which are given:- off -by;itli'e hotter parts of theapparatus,

the general direction-of the reaching the cold walls of accumulatinguntil-some flow sends an. eddy or gas into a 'region where back-fire mayoccur. ;In

l.my.:..vapor-blastcontrol system, a gas-free blast.

of vapor from the cathode :is-definitely directed across the anodes, andparticularly across the mouths of the anodeshields,-where such shieldscentral l2 cooled by water which entersthrough an inlet areutilized,-so'as ..to carry alongany foreign There is "another factor inthe behavior of a h v rectifier which has to be taken into account indetermining 'the amount. and density of vapor current flowsf'in an anodeshield to theanode -head,-the vapor in theshield is heated and tends vat'thebottom of the "shield; When the current flow ceases, the vaporre-enters""the anodesh'ield due'to the reduced temperature lof the gasinthe shield. 'I'his renecessary in the auxiliary stream. When the toexpand and. flow out sults' in a'breathing-efiect which tends to drawinto the shield whatever. vapor may surround theopening, just atithetime when the'neg'ative potential is being applied." It is .thusnecessary that the vapor-surrounding the opening of the fanon ie'vshield shall, .be' to a sufficient extent unionized, Doubtless the;preach the proble'rn of determining the amount only way forlus to ap- Ihavebeen able, as described in the present application, to obtain ablast of sufiiciently un-ionized vapor. from thecathbde pool itself,without resorting central blast from th the nature and importanceofameans forincreasing the" central blast,

which lies in the direct arc'path between the cathode and 'thefsev'eralanodes. also showswhat is now my preferre'dmethod of controlling thetemperatures of the various coolthe section plane being indicated on theline IV- IV; I V W Fig; "5 is a partial vertical, sectional viewtureresponsivedevice associated therewith.

"continually being the tank to which the aroundthe upper portion of-bafiie l2 and above the conical bafiie i3. Each I.J.. T. Mathews SerialNo. .26, 1932 and assigned is the use'of a quartz v anodelead or shank263 and counter-sunk into the anode head i6." Surrounding the quartztube l9, and resting'upon the top of the anode head 96,

i the lower end of space, as well. as

I 7 2,011,605 fier constructions shownin my copendingappli cation justmentioned, use was made of a separate mercury pool, heated by anauxiliary source,

of auxiliary vapor flow which will be required will be by trial, atleast for the present.

With the foregoing and otherobjects in view, my invention consists inthe various structures, combinations, [methods and arrangements of partswhich are hereinafter described and claimed and shown in theaccompanying drawings, where- Figure l is a sectionalview of a rectifierembodying my invention in a form which utilizes cathode pool itself,with a series connection 'of the various coolers for the purpose ofobtaining proper maintene'nce of the blast.

Fig.2is a'similar View showing the use of an auxiliary mercury pool orauxiliary portion of the mainpool which is segregated as the source ofthe un-ionized blast.

' Fig. 3 is aview similar to Fig. 1, illustrating the relative strengthof as compared to the radial blast This figure ers, with automatic meansfor this purpose.

,Fig. 4 is a sectional view of the center cooler, F 3 by through thecenter cooler, showing the tempera- Fig'. dis a diagrammatic Viewillustrating the water flow system for the'coolers, 1 In'Fig. l'myinvention is shown applied to a metal-tank rectifier comprising a maintank portion! having an insulated cathode receptacle 8 in the bottomthereof. Ajliquid mercury cathode pool Bais disposed in the-bottom ofsaid cathodereceptacle 8. The side and bottom walls of the" tank areprovided? with a tank. cooler or water jacket 9 'and the cathodereceptacle is :provided with a water'jacketor cathode cooler i9.Depending from the central portion of the 'coverplate H of the tank is acentral cooler or tubular baffle l2 hich terminates, atits lower 'end,in an annular conical baiiie l3. Both the and the conical ba'file 53 arepipe l' liand leaves through-anfoutlet pipe vl5.

A "plurality 'of anodes fiii'are'disposed in a ring the centraltubularanode may be providedwith I an anode shield H,

:the bottom ofwhichis protectedby a grid 18.

also, I-utilize an anode construction Preferably, as shown and claimedper se'in an application of 588,915, filed January to. the WestinghouseElectric & Manufacturing Company. One of the most significant thingsabout-this anode construction tube l9 surrounding the is a quartz'discor ring 2! which is spaced from the anode porcelain 22. This the quartztube, i9, seem to be necessary, in addition tothe arrangement of thefmercury blasts in my .present ap plication, in order to secure thefullest measure of freedom from back-fires which .has .tofore.

'not f been attainable herethe approximate temperature gradients whichare necessary for the or thermostat which is The ring of anodes' lfi isdisposed close in to- Wards thecentercooler I2, being much closer to'said coole'rthan to the side walls of ,the'tank l. Surrounding'the ringof anodes is an intermediate cooler 24', and surrounding that there maybean outer cooler 25. The outer cooler 25 and the tank cooler 9 providewhat I call the final con-- Toy "and leaves it at a Y with thevelocity.'

, densing walls; or

surface of the mercury,

, ing a downwardly and walls of which the predominant characteristic isthatthe mercury condenses and runs as a liquid back to the cathode, asdistinguished from a wall on: which the mercury condenses andre-evaporates." For brevity, I shall refer to these. final condensingwalls as the side walls of the tank 1, regarding the outercooler 2'5,

if it'is used, as simply a continuation of the side walls of the tank;To make my meaning more clear, I shall refer next to the temperaturegradients which I maintain within the tank, and to the general phenomenaof mercury vapor flow.

1 Mercury vapor leaves the cathode at a high velocity, probablymuchhigher than the velocity corresponding merely to the temperature ofthe although this temperaof the mercury vapor ture is the. hottest partblast; As soon as the mercury vapor leaves the cathode surface, itexpands with molecular movements in all. directions, but with apreponderance of the molecules or particles moving in the direction' ofthe temperature gradient, ortowardthecooler portions of the rectifier.When mercuryvapor touches the central cooler, which, according tomyinvention, is the hottest cooling surface, being intermediate intemperature be tween the temperature of the surface of the meri curypool and the temperature of the final condensing walls, the vapor"approaches the surface of i the cooler at the high velocityabovedescribed much lower velocity corresponding to the molecularvelocity corresponding to the temperature of the cooler. I describe thisprocess as a condensationandcre-evaporation of the mercury on the wallsof the cooler. During this process, the vapor also loses the ionizationwhich it had when ode.

it left the region of the cath- In its progress up through the. [centralcooler l2, the mercury vapor thus becomes deionized and it loses much ofits velocity and, of course, much of'the vapor pressure which goes Whenthe central blast of mercury vapor reaches the top of the centralcooler, itiagain expands, as afree gas which is released, underpressure, in a space,in a manner similar to that which was described forthe blast astitifirst left the mercury cathode. Some of the mercuryvapor comes down and condenses on the top walls of the ,conicalbafiiel3, and some goes out totheintermediate cooler 24, therebyprovidoutwardly directed blast of'substantially un-ionized mercury vaporwhich is fairly free of foreign gases, sweeping past the bottom mouthsof the anode shields l1, and carrying along with it any foreign gaseswhich are liberated from the anodes l6.

In'addition to-the central blast which rises from, the cathode, there isalso .a radial blast which passes outwardly under the conical baiiie i3and thence out to the side walls of the tank and to the outer cooler 25,the two blasts joining and condensing, finally upon the final condensingwalls of the tank cooler 9 and the outer cooler 25. r Y

In order to maintain .the vapor flow just described, it is essentialthat the central cooler shall have a temperature cooler than the initialtemperature of the vapor blast, so that the mercury vapor will condenseon it, and yet warmer-than the final condensing walls, so that theexpanding vapor, as it loses its velocity and pressure, willre-evaporate and move onas un-ionized vapor. The intermediate cooler atemperature more nearly like that of the inner cooler l2.

In the particular system shown in Fig. 1, the approximate temperaturegradients of the coolers are maintained by introducing the cooling waterfirst into the cathode cooler in, as indicated by the inlet pipe 30. Thewater leaves the cathode cooler 10 through 'a rubber hose connection 35and entersthe inlet pipe 32 of the tank cooler 9. It leaves the tankcooler through the outlet pipe 33 and enters the outer cooler 25.Leaving the outer cooler through the outlet pipe 35, the cooling waterthen enters the intermediate cooler 2 rom which it passes, through pipes36,,to the inlet pipe #4 of the central cooler l2 and conical bafflc l3.The water leaves the central cooler i2 through the outlet pipe l5 andenters a coverplate cooler 38, from which the water is dischargedthrough a suitable outlet or drain pipe 39. In the foregoing system ofwater connections, it will be observed that the hottest water is atthe'inner cooler l2 and that the coldest water is in the tank cooler 9and the outer cooler-25.

The above-described scheme of controlling the temperatures at thevarious parts of the rectifier so as to produce the conditions necessaryfor the vapor to flow from the cathode to the cooling surfaces, throughpaths apart from the danger zones, (the regions of the anodes whereback-fires are likely to occur, is very important in reducing thefrequency of these back-fires. The particular structure shown in Fig. 1illustrates the principle, although I do not believe that it carries itout as far as possible, For example, if we make the center baffle hotterby, say, 10 degrees, than the balance of the condensing surface, thenthe vapor pressure just at the surface of this baffle is approximatelytwice as high as the vapor pressure at the cooler surfaces. Thiscertainly produces a tendency for vapor to flow from the center bafileto the cooler surfaces and this vapor, flowing in thisdirection, willcarry foreign gases and ionized mercury vapor with it toward the maincondensing surfaces and thus into pieces where less harm is done. t is,of course, necessary that the hot walls be cool enough to ensurecondensation, so that saturated mercury vapor will be present.

I also find'that the groupingor nesting of'the anodes l6, close intowards the center cooler if,

has an important bearing on the freedom from back-fire. In other words,it is important to provide a free radial space between the ring ofanodes 7 l6 andthe side walls of the tank 1. This is pari the bottom ofthe intermediate cooler and out to the side and bottom walls of the tank7. I

' The main arcing path between the cathode and the several anodes isaround thecentral conical baflle l3, although it must be understood thatthe arc, taking place, as it does, in an extremelylowpressure gas orvaponspreads out pretty largely over the wholetank space, some of itprobably even 26 should, I believe, have 2' passing .at leastoccasionally, through the cen a tral'blast path hereinabove described."-

A further point to be considered is'that the v2 c-' uurn pumpingconnectionqshouldbe arranged so as to open'into the tank at the pointwhere. the gases accumulate.

In the present: rectifier, as above described, thispoint isat the. topof the side walls of; the tank portion. l;

i inear the side walls :of the tank, inFig. 1.

I have found some indicationoi a. tendency oi the design'shown in Fig.1to be sensitive torapidly applied loads.

While thenurnber of arc-backs is relatively small, all of thearc-backswhich-have mercury pool spread occurred soiar have occurred at a timewhen the loadfwas suddenly increased, say, from 25% of full load to 260%of full load, the frequency of I back-fires, under such circumstances,being about one in' a thousand times.

iew minutes; after such an increase :inloadthe arc dropis considerablyhigher and is considerably erratic.

. I; also find that, for a I attribute these phenomenan ainlyto theslowness with which the cathode spotsonthe out over the surface of thepool, so as to carry the time which it takes for the average temperaturegof the top surface the mercury pool to increase-teavaluenecessary to supp y the increased mercuryvapor which is necessaryto be present inthe arc 'paths. In other words,

the central blast, in the particular design shown,'

does not seem' to-be large enoug to supply. a 'suf-f ficient number ofuneionized mercury molecules or vaporin the, regionunder theanodeshields ll,

' sothatthere arenot sufiicientgas'particles there. j to carry theincreased load current without excessive arc drops. i

* There are .twoways 'in which might correct this'defect, according to"my prese'nt theories.

- baffle 43 is provided between the central cooler 12' i and a centralportion 0 the mercury pool, which is heat-insulated from indicated at M.A heatert l is provided ior this One isto utilize an auxiliary source ofmercury vapor, for theun-ionized last, :as I haveindif cated in Fig. 21"Inthis case; atubular quartz thev cathode cooler 19, as

1 0 wh r byfmer u fmar-be central .mercury boiled off therefrom vatanyrate which maybe form of embodimentof vmy indesired. In this'vention, one or more starti 'g'anodesf it are provided, in the outeractive annular portion of the I mercury poolil'l-"instead of usingasingle cen trally located starting anode {it as inthe Fig. I

construction. Fig; 2""a1so showsafeature which-may boot utility in anyof the forms-f embodiment'o'fmyj invention, namely, a depending tubularibaffle 59 creased central mercury of thej'ring'oi anodes depending fromthe mouths of the anode shields ll.

An additional method oi' obtaining" the? in endoi thecentral'cjoolerfltd isfjopenedouthke,

a tunnel, as indic'atediat 51, ,so that itsp'reads oversubstantiallythewh'ole area oiithe cathode pool, so as totake instant advantagejofthe increased mercury ebullitionjrom the'regiojns of V the cathodespots, no matter in load. Inthis way, it is believed that moremercury'vapor will immediatelypassup through" the'centralbafileor'cooler 12,without waiting 7 h o o I haveindic'ated a j vacuum pumpingconnection l l'in the cover plate 1 1'0 the increased load, and to 7 41;cover plate l tin the region, 3 l6 ior'the purpose of assist;- ing" indirecting the'blast downwardpast the I blast which I believe to beneeded in'the particular designshown in f e Fig. l, is indicated inFig.fi wher'ein the bottom I v where they arelo ated, upon the occurrence ofa sudden increase for the temperature .of the cathode, spotsfto spreadout over thesurface ofthe mercury,upon

the occurrence of.asdddenincreaseiin load." I

. Figure 3.-also shows what I nowlbelievev tobe the bestwatercirculating systemin the coolers.

As in Fig. 1, the coolers are connected in series,

' althoughin the broadest aspects of 'my' invention I am not to belimited toaiseries connection.

InFig. 3, however, the cathode. cooler i0 is placed in thethird positioninsteadofiihthe first positionv in. the series oi jco'olers whichconstitute .the

path or thecooling watenandwl provide means for artificially heatingallot the. coolers except the tank'cooler 9 and the outer cooler25,'during periods of no load," so that the parts arekept at atemperature suitable for immediate assumption ofload. j 2. As shown in-Fig. 3,"as Wellasinthe diagramvalve or" so-called water-flowregulatorllland thence'tothe'tankcooler 9 and outer cooler ZEl. Fromthefdischarge pipe 350i the outer cooler, a

hose connection 72 leads bothptoithe' cathode cooler ID and to a heatertank'le. Tracing first the normal-path of the water through the cathodecooler, a second hose, connection 116 carries the water to theinletpipe? of the. intere center cooler and-the cover-plate to theoutlet pipe 39 which is connectedboth to the drain Ti "and totheinletside of a pumpf-lawhich, when operatinggdischarges water into the heatertank .HLirom which it is. recirculated .thrOughthe cathode,intermediate; center? and "cover-plate I coolers" H3, 2t, "ltwand 38;.The pump 19 is adapted to be driven by -a .motor:8 l which may beenergized, whenever current is supplied to. an

electric heater 53in the heater tank i l, in re-' sponse to theoperationof a contactor switch 8d. It will be understood that, normally,whenithe the electric water heater- 83 and the pump'l'fi 'will beunenergized, so'that no water will flow therethrough.

To give some 'idea of the temperatures involvedy l shall indicatecertain temperatures which'ha've been found-'to' be satisfactory, al-.though it willbe understood thatI am not to be 'matic viewpf Figw6,water isiled first through'a mediate cooler 2d, whence itpasses throughthe altogether limited tothese particular tempera-- I tures, Inlet wateris supplied,at almost any desire able temperature, which preferablyshould be lessthan 35 0., as indicated in Fig. 6. After passing throughthe tank cooler, a water, temperature of as large as 40 C'. may beutilized. The'waterwill be slightly furtherheatedcinpassing through thesol outer'cooler; reaching a. temperature of possibly Subsequently, thewater temperatures will be- 42, at the end; of thecathode cooleri 45;at

the end of 'theintermediate .cooler; 52 at the end of the center coolerand possibly. 55 at the discharge terminal 39.*rThese teniperatures' aremerely given for 'illust ative purposes,

During periods of no1oad,; or extrem'elylight loads, .it is verydesirable to'preventthe temperatures; of the cathode and of theintermediate and center coolers-from falling totoo low a value.

I, thereforaprovide means 'for shutting ed the water-flow regulator" l8andfstarting' 'an inter mediate circulationfby means of the pump heatertank, as previously described. In such a case, the inlet water which isfed first to the cathode cooler from the heater tank may have atemperature ,ofabout '51? C., after which it is conducted intotheintermediate cooler at a tern perature of, say, 48 0., then to thecentercooler and I rectifier tank is carryingany appreciable load, t

Bands and contracts in .the pump motor 8|.

. ga'gement of the contact finger 92 plate at a temperature of 47,returning to the pump at a temperature of possibly 46 C., from whichitis discharged againinto the heater tank 74. I

It will be observed that, at alltimes, the intermediate and centercoolers are kept at a temperature intermediate between that of thecathode surface and that of the tank cooler and outer cooler, so thatthe vapor fiow, as previ ously described, may be satisfactorilymaintained.

It will also be observed that the principal source sensitive to loadchanges.

y In devising an automatic heat control system, therefore, I utilize athermostat or heat-responwhich is responsive to the water temperature inthe center cooler I2a. As shown in Figs. 4 and 5, this heat-responsiveelement may take the form of a liquid container which is inserted in thecenter cooler |2a and which is connected, externally of the tank, bymeans of a pipeconnection 81, to a metallic bellows 88 which exresponseto temperature changes in the center cooler. This metallic bellows ismounted as an integral part of the waterfiow regulator, so that it turnsoff the water at a temperature of, say, 50 in the center cooler, andturns it open wide at. a temperature of 58 C. in the center cooler.

' Upon either the same or a duplicate thermostatic device 86, 88, aninsulating support 89 carries a contact finger 90 which moves betweentwo stationary spring-contact fingers 9| and 92. Energy is supplied froma relay battery 93 to the movable'contact finger 90, so that when theback contact 9! is engaged, at a temperature of, say, 45 C.,' thecontactor switch 84 will be energized in order to turn on the waterheater 83 and As soon as the contactor switch 84 picks up, a holdcircuit 95 is ener' gized through the normally closed contacts 96 of anauxiliary relay 97 which is tripped by the enat a temperature of, say,48 C., so that the water heater and pump are cut off at. thistemperature. Whenthe temperature of the central cooler l Zincreases twomore degrees, or to 50 C., the thermostatic device begins to turn onthe'water-flow regulator, as previously described.

very excessive temperatures should be reached, a final limit-switchcontact 98 is reached, by the contact member 99 of the thermostaticsuccess of'a sectionalized-type design which constitutes the subjectmatter of my copending application Serial No. 589,414, filed January 28,1932.

sectionalized design isa. much smaller size than has heretofore beenpossible. I feel that it is the herein-described control of thedirectionand magnitude of the fiow of mercury vapor within the rectifiertank, which has made it possible for me to provide a rating of 750kilowatts at 600 volts in a volume only one-half as great as haspreviously been required for a 500 kilowatt rating at 600 volts.

While I prefer to utilize an automatically controlled temperatureregulation in the various I contemplate that numerous changes will bemade within the scope of my invention, such as the possible eliminationof a part of the shielding around the anodes, which would result in afurther reduction in internal losses. I have also obtained a materialgain in efliciency by utilizing a 2" depth for the cathode receptacleinstead of an 8" depth.

tion is increased by my vapor-flow means for preventing back-fires, thusmaking it possible to dispense with many of the shields and otherobstructions which have been heretofore'needed for the purpose ofpreventing back-fires and which consume several volts of arc drop. 'Forexample, previous Westinghouse designs of 500 kilowatt rectifiers, aswell as present competitive designs of the same capacity, have afull-load arc-drop of approximately 21 volts. The design shown in Fig.1,..which is now in service, has a full-load arc-drop of 20 volts, at a50% increase in rating over the previous and competitive designsof twicethe size. An experimental modification, making full use of the principlediscussed hereinabove, has been made and tested and found, so far as therestricted tests indicate, to be satisfactoryyhavihg a full-loadarc-drop of approximately 16 volts. I believe that a reduction in theanode shielding and an increase in the central blast over that shownin'Fig. 1 will reduce the full-load losses to possibly 13 volts.

In connection with the disposition of foreign sembly. My own experience,as well as that of others. has clearly shown that the quality of arectifier may be determined by the degree of freedom from foreign gases.In building my rectifiers, I go to rather extreme lengths to decreasethe amount of foreign gas. One of the most important items in thisregard is the practide of high-temperature pre-treatment of the graphiteanode-head under vacuum. All other materials which might emit foreigngases are pro-treated before assembly wherever this can reasonably bedone.

A practice which I believe is novel in metaltank rectifiers is todetermine the completion of the treating-out process by a measurement ofpressure-rise within the rectifier at a maximum contemplated loadcurrent for a given period of time, with the pumps not in operation. Theprevious practice of treating until a given degree of vacuum could bemaintained by the pumps did not give complete information as to thecondition of the rectifier from the standpoint of freeof said centraltubular' bafile, also spaced from the'cathode, a plurality of anodesspaced in apresncd' of foreign gas,

10 stitute of? Electrical! Engineers on January' 28,

- the cathode, a iplurality'of circle close "touthe upperportion: ofsaid central tubula'rsbafile and for the-most part. over said dom from 1ooclude'd '1 'g'ases i- I have found that:

even though a high'degree 10f vacuum may be maintained by: the operationrectifier from the hot surfaces 'to'the' pumping connection, isdefinitely and seriously detri mental.

:.The subject-matter of the present application is more or lesscompletely shownand discussed in my "paper presented beforethe AmericanIn- Iclaim; as my invention:

.1.'A multi-anode, metal-tank, mercury arc rectifier characterized by1.'a central tubular bafile cverthe cathode in spaced relation thereto,an}- annular bafile'mountedi around the bottom end QfT said centraltubular.

the cathode, a'plurality "of anodesspaced in a qcircle'close to' theupper portion of "said central tubularbaflle and fo'r'the most part oversaid annular, baille, and a second tubular baffle suriroundingsaid-circlefof anodes. J

2. A multi-anode, metal-tank,umercury-arc rectifier character-ized'by acentral tubular bafile overthecathode in, spaced relation thereto, anannular-baffie mountedaroundithe bottom end of saidicentral tubularbailie, also spaced from anodes spacedin a annular baffle, and aliquid-cooled jacketior said central tubularbafile;

over the cathode in spaced relation thereto, an annularbafiiefimounted'around thebottom end of said central tubular baffle,a1sospaced from the cathode, a plurality of anodes spaced in a cooledjacketior the tubular liquid-cooled jacket for the side; walls of saidtank. i a

, rectifier characterizedby'a central tubular bailie circle close to theupper portion ofsaid central tubular baffle and for the most part oversaid annular baflie, a tubular ,bafile; an annular liquid top of saidtank, and a said central tubular '4. A -multi-anode, 'metal-tank',mercury-arc over the cathode in spaced relation thereto, an annularbafilemounted around thebottom end circle close to the upper portion ofsaid central tubular baffle andfor the" most part over saidannularbaflle, a second tubular 'bafile surrounding said circle ofanodes, a tubular liquid cooled jacket for said central tubular bafile,a tubular liquid-cooled jacket for said second tubular baflie; anannularliquid-cooled jacket for 3 the top of said tank, and atubular'liquid-cooled jacket for theside walls-of said tank. r r

5. A multi-anode, metal-tank, mercury-arc rectifier characterized by acentral tubular baffle 7 the cathode; a plurality over the cathode inspaced relation thereto, an:

annular bafile, mounted around: the, bottom end of said central tubularbaffle, also spaced from 1 of anodes spaced in a circle close to theupper portion of said central tubular baffle land for the'fmost partover said annular baffle,and an individual shieldand grid for each ofthe anodes.

; 6. A multi-anode; metal-tank, mercury-arc rectifier comprising a maintank, an insulated, centrally disposed, cathode-receptacle in" thebottom thereof, liquid mercury in said cathodeof" the.pumps,. the. bularbaffle in spa'ced .fiowing through the bafile, also spaced from rcury-vapor flow path metal-tank, mercury-arc rectifier characterizedby'a centraltubular baflie liquid-cooled jacket for receptacle,

a centralvertical ftubular baffle, an!

annular baffle mounted" around said central. tu-;

said annular baffle and at of said central tubular bafiie, and apluralityj'of anodesspaced around said central tubular bafile" abovesaid annular baflie.

'1; A multi-anodaj metal-tank, *mercuryearc rectifier 'comprisinga maintank, an insulated,

' centrally. disposed, cathode-receptacle inthe bot-v tom thereof,liquid mercury in saidcathode-rew;

' as, reducing the vapor-pressure of, a mercury vapor flow from, theliquid mercury centrally upward and out past the regions of the anodes,and an annular baflie surrounding the central meranddisposed between theregions of the anodes and the bottom of the tank forproviding arelatively ionized f'main arc-path,

under said annularbafiie.betweensaid regions of said anodes and saidcentrallyv disposed: liquid mercury. T r v L '1,

'8. A lrnulti-anode, metal tank, mercury-arc rectifier characterized bya'central tubular baffle over the cathode inspaced relation thereto, anannularbafile mounted arourldthe bottom end of said central tubularbaffle, alsospaced from the cathode, aplurality'of anodes-spaced inv a:circle close to the upperpor'tionof I said central tubular balTle' andforthemost part :over saidannular baiile, a liquid-cooledjacket for saidcentral tubular ballle and-for said annular battle and an aux,-iliary-tubular'bafile depending iro'm'said central liquid-cooled baffle.1' I ,9. "A ,multi-anode, metal-tank; "mercury-arc rectifiercharacterized by an insulated cathode re ceptacle, a-rnercury'catho-detherein, acentral tubularbaffle' over thecathode in spaced relationthereto, an annular; baflle mounted around the bottom end of said'central tubular baffle, also spaced from the cathode, a plurality ofanodes spaced in av circle close to the"upper portion of saidlcentraltubular shafts and forv the most part over said annular battle-[a secondtubular'bafile surrounding said ci'roleo'fi anodes, liquid-cooledjack'ets'for the cathodefreceptacle, for an of said the side walls ofthe tank, and an from said therebetween, from said cathode pool,said-blastproducing means comprising a'coolerfor the outer tank walls,lacooler for the annular space surrounding said anodes, and acooler forthecentral space'over said-cathodep'ool and within theliquid-cooled'baffie.

1l. A multi-anode, metal-tank, mercury-arc rectifier characterized by a"central tubular baflle relation to the liquid mer-;; jcury, acirculating liquid cooling-mediumkforleast the top portion annular spaceoccupied by said anodes, said firsta V ,mentioned cooler being overthecathode-in spacedrelation thereto, 'an

annular baffle mounted around thebottom end of said central tubularbaffle, also spaced from the cathode, a plurality of anodes spaced in acircle close to the upper portion of said central tubular bafiie and forthe most part over said annular baifie, a liquid-cooled jacket for saidcentral tubular baffle, means for substantially segregating the surfaceof the central portion of the mercury cathode from the annular outerportion thereof, and a heater for said segregated central portion.

12. A multi-anode, metal-tank, mercury-arc rectifier comprising a maintank, an insulated,

centrally disposed, cathode-receptacle in the bottom thereof, liquidmercury in said cathode-receptacle, a central vertical tubular baflle,an annular baffle mounted around said centraltubular bafile in spacedrelation to the liquid mercury, a circulating liquid cooling-medium forsaid annular bafile and at least the top portion of said central tubularbaffle, a plurality of anodes spaced around said central tubular baffleabove said annular baiile, means for substantially segregating thesurface of the central portion of the mercury cathode from the annularouter portion thereof, and a heater for said segregating centralportion.

13. A multi--anode, metal-tank, mercury-arc rectifier comprising a maintank, an insulated, centrally disposed, cathode-receptacle in the bottomthereof, liquid mercury in said cathode-receptacle, a plurality ofanodes spaced in a circle in said main tank, means, including acirculatingliquid cooling-means disposed in the central space of themain tank, for largely deionizing, as well as reducing thevapor-pressure of, a mercuryvapor flow from the central portion ofliquid mercury centrally upward and out past the regions of the anodes,an annular baifie surrounding the central mercury-vapor flow path anddisposed between the regions of the anodes and the bottom of the tankfor providing a relatively ionized main arc-path under said annularbaflle between said regions of said anodes and said central portion ofthe liquid mercury cathode, means for substantially segregating thesurface of the central portion of the mercury cathode from the annularouter portion thereof, and a heater for said segregated central portion.

14. A multi-anode, metal-tank, mercury-arc rectifier having a liquidmercury cathode pool, a plurality of anodes, there being a main arcpathbetween the cathode and the several anodes, and means for producing ablast of relatively un-ionized, low-pressure mercury vapor blowing overthe regions of said anodes and the arc-back spaces therebetween, fromsaid cathode, said blast-producing means comprising a cooler for theouter tank walls, a cooler for the annular space surrounding saidanodes, and a cooler for the central space over said cathode pool andwithin the annular space occupied by said anodes, means forsubstantially segregating'the surface of the central portion of themercury cathode from the annular outer portion thereof, and a heater forsaid segregated central portion.

15. A multi-anode, metal-tank, mercury-arc rectifier having a liquidmercury cathode pool, a plurality of anodes, there being a main arc-pathbetween the cathode and the several anodes, and means for producing ablast of relatively un-ionized, low-pressure mercury vapor blowing overthe regions of said anodes and the arc-back spaces therebetween, saidblast-producing means comprising a centrally disposed source of mercuryvapor segregated from the active annular cathode surface of the mercurypool, and a succession of coolers in the path of the blast from saidmercury-vapor source, past the region of the anodes, and on beyond tothe outer walls of the tank, terminating in a cooler at said outerWalls, a cooler which is disposed in the path between said mercury-vaporsource and the region of the anodes being at a temperature intermediatebetween the temperature of the outer-wall cooler and the highertemperature of the mercury-vapor source.

16. A multi-anode, metal-tank, mercury-arc rectifier characterized by acentral, cylindrically disposed cooler, a ring of anodes surrounding thesame, an intermediate, cylindrically disposed cooler surrounding thering of anodes, a cathode cooler, a tank cooler for the side walls ofthe tank, a main circulating system for supplying a liquidheat-interchange medium in series through the tank cooler, cathodecooler, intermediate cooler and central cooler, in said order, startingwith the tank cooler, a liquid-flow regulator for said main circulatingsystem, and an auxiliary circulating system comprising a heater andmeans for circulating the liquid heat-interchange medium in seriesthrough said heater, the cathode cooler,

the intermediate cooler and the central cooler, in said order, startingwith the heater.

17. A multi-anode, metal-tank, mercury-arc rectifier characterized by acentral, cylindrically disposed cooler, a ring of anodes surrounding thesame, an intermediate cylindrically disposed cooler surrounding the ringof anodes, a cathode cooler, a tank cooler for the side walls of thetank, a main circulating system for supplying a liquid heat-interchangemedium in series through the tank cooler, cathode cooler and centralcooler, in said order, starting with the tank cooler, a liquid-flowregulator for said main circulating system, an auxiliary circulatingsystem comprising a heater and means for circulating the liquidheatinterchange medium in series through said heater, the cathode coolerand the central cooler, in said order, starting with the heater, andautomatic thermally responsive regulator-means responsive tosuccessively decreasing temperatures for shutting off the liquid-flowregulator and subsequently turning on said heater system, and vice versafor'increasing temperatures.

ALFRED L. ATHERTON.

and auxiliary circulating

